A heavily loaded vehicle tire comprises a crown part surmounted radially on the outside by a tread intended to come into contact with the roadway, this crown part extending radially inward by sidewalls ending in bead structures. A pneumatic tire comprises a plurality of reinforcement armatures including, in particular, a carcass reinforcement for supporting loads created by the tire internal inflation pressure and the vehicle. This carcass reinforcement extends into the crown and the sidewalls of the pneumatic tire and is anchored at its ends to appropriate anchoring structures located in the bead structures. A carcass reinforcement may be generally made up of a plurality of reinforcing members arranged parallel to one another and making an angle of, or in the region of, 90 degrees with the circumferential direction (in which case, the carcass reinforcement is said to be “radial”). The carcass reinforcement is usually anchored by turning it up around an anchoring structure of appropriate circumferential rigidity in order to form a turned-up portion of which the length, measured for example with respect to the radially innermost point of the anchoring structure, may be chosen to provide the pneumatic tire with satisfactory durability. Axially between the turned-up portion and the carcass reinforcement may be one or more elastomer-based materials which provide a mechanical coupling between the turned-up portions and the main carcass reinforcement.
In use, the pneumatic tire may be mounted on a rim with rim seats intended to contact the radially innermost parts of the bead structures. On the axially outer side of each rim seat, a rim flange may fix the axial position of each bead structure when the pneumatic tire is fitted onto the rim and inflated to its normal operational pressure.
In order to withstand the mechanical stresses of rotating under load, additional reinforcements may be provided for reinforcing the bead structures. For example, plies may be arranged against at least a part of the turned-up portion of the carcass reinforcement. During use, the bead structures may be subjected to a great many bending cycles, thereby conforming/deforming themselves to the rim flanges (e.g., partially adopting the geometry of the rim flanges). This results in greater or lesser variants in curvature of the bead structures combined with variations in tension in the reinforcement armatures that reinforce the bead structures and, in particular, in the turned-up portion of the carcass reinforcement. These same cycles may induce compressive and extensile loadings in the materials of the bead structures. Also, the reinforcing members of the carcass ply may shift circumferentially and cyclically in the sidewalls and the bead structures of the pneumatic tire. A cyclic circumferential shift is a shift in one circumferential direction and in the opposite circumferential direction each time the wheel and pneumatic tire revolve about a position of equilibrium (or no shift).
Stresses and/or deformations may be generated within the materials of the bead structures, and particularly within the elastomeric materials in the immediate vicinity of the ends of the reinforcements (the ends of the turned-up portions of the carcass reinforcement, or ends of the additional reinforcements). These stresses and/or deformations may lead to an appreciable reduction in the operating/service life of the pneumatic tire.
These stresses and/or deformations may cause delamination and cracking near the ends of the reinforcements. Because of the radial direction of some of the reinforcing members and because of the nature of the reinforcing members (e.g., metal cables), the turned-up ends of the carcass reinforcement may be particularly sensitive to this phenomenon.